Process of treating aluminium articles for the formation of galvanic metallic coatings.



tallic alloy an extremely adherent coating UNITED STATES,

PATENT oFF IoE- CARL RUMPLER, or sononnenne, NEAR BERLIN, G RMANY.

rnoonss or TREATING ALUMINIUM ARTICLES FOR; THE FORMATION or GALVANiC METALLIC COATINGS.

No Drawing.

Specification of Letters Patent.

To all whom it may concern:

Be it known that I, CARL RtiMrLER, merchant, a subject of the King of Prussia, residing at Schoneberg, near Berlin, Germany, have invented certain new and useful Im-' provements in an Improved Process of,

'lieating Aluminium Articles for the Formatlon of Galvanic Metallic Coatings; and

I do hereby declare the following to be a full, clear, and exact description of the in vention, such aslwill' enable others skilled in the art to which it appertains to make and use the same. I The present invention relates to an improved process of-formi'ng galvanic metallic coatings on aluminium and consists in preliminarily freeing the aluminium article to be treated from grease or the like, cleaning it and then providing it in a preliminary bathwith a thin film-like coating upon which any desired metallic coating may be deposited in the usual electrolytic baths employed for ordinary metals.

The essential feature of the present 'invention may be said to consist 1n the fact that the film-like deposit, which forms the .basis for the actual metallic coating to be sililbsequently deposited, consists of a metallic a v- It has been found. thatbyemploying a mean adequate quantity of sulfitebeing added to the bath in order to prevent oxidation of.

the cyanid. It is also advantageous to add to the bath a small quantity of a salt having an alkaline reaction such for example as potash or soda. This solution however deposits a brass very rich in zinc anda coating of this is less adherent than if the 'alloyis poorer in zinc. The precipitated alloy should preferably contain not less than of copper. Now it has been found that-in order to obtain a deposit containing a suffi- -cient percentage of copper it is-necessary to add a small quantity of an alkaline haloid such for example as chlorid of potassium. or

iodid of potassium.

Good results are obtainedv with a preliminary bath of .the following. composition: '1 liter of water. 4060 .of copper. 15-30 gr. of double cyanid of zinc; 108'0 gr. of commercial sodium sulfite; 10-25 gr. potash. 210' gr. fchlo- Patented May 16,1911. Application and October 0, 1910. sem No. 585,681. Y

gr. of double. cyanid rid of potassium. For the double cyanids it is advantageous to employ the respective metallic salts with cyanid of potassium solution until the cyanid deposit formed is dissolved. 1

The anodes may be of brass or of copper and zinc anodes, oronly copper anodes can be used,in which latter case, however, it is frequently necessary to regenerate the. bath and replenish the double zinc cyanid. If the brass is to adhere Well, in the first place it is essential to maintain a suitable voltage. 1

The voltage depends upon the halogen ion employed. It'must be highest when chlorid is present, say approximately 1.8 volts; bromid requires approximately 1.7 volts; iodid approximately 1.6 volts. It is advisable to have a current strength of from 2 to 3.6 am'peres'per square decimeter. The .pe-

riod for the formationof the thin film-like coating-of metallic alloy on the aluminium may amount to from a minute to 2 minutes. Preferably the article is only exposed to the current in the electrolyte for a period of substantially one minute.

Having now particularly described and ascertained the nature of my said invention .and in what manner the same is to be performed, 'I declare that what I claim is 1. A process for conditioning aluminum articles for the deposition of metallic coat ings by electrolytic baths which conslsts in treating the article electrolytically 1n a bath comprising an aqueous solution of two or more metallic double-cyanids, and-'a sulfite to prevent oxidation; as set forth.

2. A process for conditioning aluminunr articles for the deposition of metallic coatings by electrolytic baths which consists in treating the article electrolytically in a bath comprising an aqueous solutlon -of two or more metallic double-cyanids, and a sulfite to prevent oxidation; by a current of from 1.6 to 1.8 volts, and a current strength of from 2 to 3.6 amperes per square declmeter; as setforth.

' 3. A process for conditioning aluminum articles for thedeposition of metallic Coat ings by electrolytic baths which consists in In testimony whereof, I aflix my signature, treating the article electrolytically in a bath in presence of two witnesses. containing double cy-anid of copper, double CARL RI'FMPLER cyanid of zinc, an alkaline sulfite, and an 5 addition of an alkaline halogen, and of a Witnesses:

salt producing an alkaline reaction such-as AN'roN PELSGHING,. potash or soda. AUGUST FUGGER. 

